Marking apparatus with a plurality of lasers, deflection means, and telescopic means for each laser beam

ABSTRACT

The invention relates to a marking apparatus for marking an object with laser light, comprising a plurality of lasers and a control unit for individually activating each of the lasers to emit a laser beam ( 90   a - i ) according to a sign to be marked. A set of deflection means ( 30 ) for directing the laser beams ( 90   a - i ) toward the object to be marked is provided, a set of telescopic means ( 40 ) comprising at least one telescopic means ( 40   a - i ) per laser beam ( 90   a - i ) is provided, and each telescopic means ( 40   a - i ) is adjustable for individually setting a focal length of the respective laser beam ( 90   a - i ).

FIELD OF THE INVENTION

The present invention relates to a marking apparatus for marking an object with laser light.

RELATED ART

Generally, marking apparatuses are known which deploy a single gas laser, e.g. a CO₂ laser. Such a laser emits a light beam which is delivered to the object to be marked. The object is moved relative to the marking apparatus on a conveyor belt. Typically, a scanning device is provided for directing the light beam on the object according to a sign to be marked. As a high throughput of objects is generally desired, the speed of the object on the conveyor belt relative to the marking apparatus should be high. However, the speed cannot be arbitrarily increased since the scanning device requires sufficient time to write the mark on the object as it passes. Hence, the speed of such marking devices is limited by the speed of the scanning devices.

The throughput can be increased with generic marking apparatuses that comprise a plurality of lasers, in particular gas lasers, and a control unit for individually activating each of the lasers to emit a laser beam according to a sign to be marked. Such marking apparatuses are described in U.S. Pat. No. 5,229,573 and U.S. Pat. No. 5,229,574.

For achieving ever greater marking speeds, marking apparatuses with a larger numbers of lasers are demanded. However, the number of lasers is hitherto strongly restricted as the size of the individual lasers results in unduly large apparatuses and also hampers the laser beam delivery to the object to be marked.

A marking apparatus with a plurality of lasers is known from GB 2 304 641 A. Emitted laser beams are redirected with a plurality of mirrors onto one focussing lens. This focussing lens focuses all laser beams onto an article to be marked.

JP 2011-156574 discloses an apparatus for manufacturing solar panels. The laser beam of one laser is split into a plurality of beams which are each directed onto a substrate with a respective focussing lens.

A carrying structure for components of a laser is known from U.S. Pat. No. 5,115,446 A.

Subject matter of U.S. Pat. No. 6,421,159 B1 is a marking apparatus with a number of individual lasers. All beams emitted by these lasers are directed on one focussing lens.

A laser device for irradiating lithographic printing plates is described in U.S. Pat. No. 5,339,737 A. A plurality of lasers is provided wherein the emitted beams are guided to predefined exit positions at a writing array. Each beam exits the writing array via a respective set of lenses.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a marking apparatus that comprises a plurality of lasers and allows for a flexible adjustment of laser beams of the lasers.

This objective is solved with a marking apparatus.

Preferred embodiments are given in the following description, in particular in connection with the attached figures.

According to embodiments of the invention, the marking apparatus of the above mentioned kind is characterized in that a set of deflection means for directing the laser beams toward the object to be marked is provided, a set of telescopic means comprising at least one telescopic means per laser beam is provided, and each telescopic means is adjustable for individually setting a focal length of the respective laser beam.

An idea of the invention resides in the provision of means for setting a degree of convergence or divergence, and thus a focal length, of each laser beam. This can be carried out for each beam separately. It is thus possible to compensate for beam path differences, i.e., different lengths of the paths the individual light beams travel until they reach the object. This may be due to the surface profile of the object or different internal path length within the marking apparatus. The object may be placed at the focuses of the laser beams or at a certain distance thereto for controlling the spot size of the laser beams on the object.

An idea of the invention resides in the provision of one telescopic means per laser beam, i.e. per laser, for collimating each beam.

In the context of embodiments of the invention, the activation of each of the lasers to emit a laser beam may be understood as any process that controls whether a light beam impinges on the object to be marked. Hence, the activation may also be carried out via a beam shutter. That is, a laser stays activated and a beam shutter controls the passing or blocking of the laser beam of the laser.

Generally, the lasers may be any kind of lasers. The invention may be advantageous if lasers in which space is critical are deployed. That is, if the laser power strongly depends on the size of the laser. Another aspect of the invention becomes readily apparent if the laser dimensions prohibit generating laser beams that are very close to each other. Embodiments of the invention also allow for a rearrangement of the laser beams resulting in a small distance between the laser beams and thus a high marking resolution.

Examples of such lasers are gas lasers, chemical lasers, fibre lasers, dye lasers, and solid-state lasers. Possibly, also semiconductor lasers or metal-vapor lasers may be employed. If gas lasers are used, these may be of any generally known kind, such as HeNe lasers, CO lasers, Argon lasers, nitrogen lasers, or excimer lasers. Preferably, the gas lasers may be CO₂ lasers. These may be operated as cw or pulsed.

The sign that is to be marked may be understood as any mark, e.g. a character, a picture or single pixels of a graphic. The sign may consist of a number of dots or lines. That is, the lasers may be activated for short periods to produce dots on the object or for a settable time span to cause lines of a certain length.

In the context of the invention, the object to be marked may be any item or product with a surface that can be affected with the light of the lasers. In particular, the object may be a packaging, e.g. for food or beverage, a fruit or a label. The material of the object may comprise plastics, paper, metals, ceramics, fabrics, composites or organic tissues.

The marking itself may be any change in the object's surface, e.g. a color change, an engraving or a cut.

In a variant of the invention, each telescopic means comprises at least two optical elements, in particular at least two lenses or curved mirrors, the distance between which being adjustable for setting the focal length. The telescopic means may thus be designed as refracting telescopes which use lenses, as reflecting telescopes which use mirrors, or as catadioptric telescopes which use at least one mirror and at least one lens. Concrete constructions of telescopes are generally known and will thus not be explained in greater detail.

The telescopic means, which may also be referred to as beam shaping means, can be linearly adjusted by the control unit, i.e. the position of at least one optical element of each telescopic means is changed in the direction of propagation of the respective laser beam.

An embodiment of the inventive marking apparatus is characterized in that the set of deflection means comprises at least one deflection means per laser beam, in particular at least one mapping mirror or one optical waveguide per laser beam, for rearranging the laser beams into a desired array of laser beams, and each deflection means is individually adjustable in its deflection direction and/or individually shiftable. That means each light beam is directed to its respective deflection means. The deflection means are adjustable independent from one another such that basically any desired configuration can be set. The light beams emitted by the lasers form a specific arrangement, e.g., a linear arrangement of light beams running in parallel. It can be seen as an essential advantage of the invention to allow for a flexible mapping of the linear arrangement into any other arrangement. In particular, the spacing between the light beams may be changed or reduced with the set of deflection means.

A preferred embodiment of the inventive marking apparatus is characterized in that the set of deflection means comprises at least one deflection means per laser beam, in particular at least one mapping mirror or one optical waveguide per laser beam, for rearranging the laser beams into a desired array of laser beams, and each deflection means is individually adjustable in its deflection direction and/or individually shiftable.

That means each light beam is directed to its respective deflection means. The deflection means are adjustable independent from one another such that basically any desired configuration can be set. The light beams emitted by the lasers form a specific arrangement, e.g., a linear arrangement of light beams running in parallel. It can be seen as an essential advantage of the invention to allow for a flexible mapping of the linear arrangement into any other arrangement. In particular, the spacing between the light beams may be changed or reduced with the set of deflection means.

The deflection means may be set to a desired position during or prior to the operation of the marking device. To this purpose, each deflection means may be displaced by an electrical motor which is controlled by the control unit. As opposed to prisms, the set of deflections means causes less distortion, particularly when mirrors are employed as deflection means.

In case of the deflection means being mirrors, the adjustment may be carried out by individually tilting the mirrors, i.e., changing the deflection directions or pointing directions of the mirrors. Additionally or alternatively, the mirrors may be displaceable, that is shiftable. As the laser beams can be re-arranged with the mirrors, the latter can also be referred to as mapping mirrors.

The aforementioned “desired array of laser beams” may be any arrangement of laser beams suited for the respective application. The desired array may be different to the original arrangement of the light beams, i.e. the arrangement prior to impinging on the set of deflection means. In particular, the desired array may be a linear arrangement that is rotated relative to the original arrangement.

According to an embodiment of the invention, the deflection means are adjusted such that a beam separation between the laser beams is reduced. The disadvantages of large beam separations due to large dimensions of the lasers may then be mitigated. Furthermore, a. high marking resolution can be achieved. In contrast to devices for reducing the beam separation in which all light beams are directed onto a common optical element, e.g., a suitable prism, the deflection means of the inventive apparatus lead to less distortion of the light beams.

A reduced beam separation also leads to the laser beams impinging more centrally on common optical elements. That can be beneficial as spherical aberration and the likes of which occur between paraxial rays, i.e. laser beams impinging on the center of a lens or mirror, and marginal rays, that is laser beams impinging far off the center of the lens or mirror. Reducing the beam separation is thus conducive to reducing spherical aberration.

Another of the invention is characterized in that the set of deflection means comprises a first and a second set of mapping mirrors, each set of mapping mirrors comprises at least one mapping mirror per laser beam, and the first set of mapping mirrors directs the laser beams onto the second set of mapping mirrors. Hence, each light beam is individually directed via at least two mapping mirrors. This may allow for a particularly flexible rearrangement of the light beams.

An embodiment of the inventive apparatus is characterized in that each telescopic means comprises a mirror which is one of the mapping mirrors of the set of deflection means and further comprises an optical element, in particular a lens or a curved mirror, which is displaceable relative to the mapping mirror. The total number of optical elements used in the inventive apparatus is thus reduced. The optical element of the telescopic means may be arranged between, prior to, or after mapping mirrors of the deflection means.

Generally, it is possible that the deflection means are manually adjustable, in particular displaceable. However it may be preferred that the control unit is adapted for shifting the deflection means and/or adjusting the deflection directions of the deflection means, in particular via gimbal mounts. For broad fields of application, each of the deflection means may be individually adjustable by the control unit. In a comparably cost-effective implementation, at least one deflection means per laser beam is adjustable by the control unit. Gimbal mounts may allow for rotations of the mounted deflection means in at least two rotational degrees of freedom or even in all directions.

The adjustment of the deflection means by the control unit allows for a variable code positioning. That means, the direction of the laser beams emanating from the apparatus can be altered to change a position of a code to be produced with the laser beams on the object. Additionally a code height can be varied.

Furthermore, a static marking is possible. In this, it is not necessary that the object is moved relative to the marking apparatus during the marking operation. The deflection means are operated to cause a scanning movement of the laser beams such that all signs to be printed are successively produced on the resting object. This embodiment may be particularly preferred for printing 2D graphics which require a high printing resolution.

The control unit may be further adapted to provide a multiple-strike option. If the laser beams are pulsed, this means that a plurality of pulses is directed onto a common spot on the object. This may be accomplished by making use of a relative movement between the object and the apparatus and by timing the firing of the lasers appropriately. Alternatively, the adjustment of the deflection means of one laser beam may be altered such that successive pulses of one laser are directed onto the common spot. A grey-scale printing is thus made possible.

The control unit may be further adapted to provide a high-power option. The adjustment of the deflection means of one or more laser beams may be altered such that the output of one or more lasers are directed onto a common spot. In this way, materials that require a higher power than a single laser can provide may still be marked. In other words, the control unit may be adapted to direct the laser beams of at least two lasers onto a common spot. For a particularly high beam power, the deflection means can be adjusted to combine any number up to the total number of laser beams.

The control unit may be further adapted to automatically adjust the deflection means to positional changes of the object, e.g. to compensate for vibrations of the object. The positional changes may be determined by a sensor such as ultrasonic or optical means or a proximity switch.

According to still another embodiment of the invention, the control unit is adapted to control the telescopic means to compensate for path length differences between the laser beams, in particular path length differences due to the arrangement of the deflection means. Depending on where to deflection means are located, the beam paths of the laser beams may have different lengths, leading to different spot sizes of the laser beams on the object. With the telescopic means a flat field correction is possible in which each laser beam has the same focal distance measured from an end side of the apparatus. It is furthermore possible to set any desired focal plane for the laser beams.

The control unit may be adapted to adjust the telescopic means in real-time when the path lengths are changed due to an adjustment of the deflection means. Additionally or alternatively, the control unit may adapted to set the telescopic means according to any information regarding a change in the path lengths, such as a vibration or any other movement of the object, or a redirecting of the laser beams with a scanning device.

An embodiment of the inventive apparatus is characterized in that at least one scanning mirror device is provided which comprises a common mirror onto which all laser beams coming from the set of deflection means impinge, and the control unit is adapted for pivoting the scanning mirror device, in particular via a galvanometer.

A scanning device or scanning mirror device may be understood as any instrument that causes a light beam to pass sequentially a number of spatial positions.

In simple cases, such devices may comprise a rotatable mirror which is rotatable around an axis normal to the plane of the incident light beam. The rotatable mirror may comprise a mirror drum, i.e., a polygon with a number or mirrors that are rotated together around a single axis.

Devices comprising a galvanometer to which a mirror is connected are generally referred to as galvanometer scanners. A galvanometer scanner may convert input electric signals into an angular position of the mirror of the galvanometer scanner, for example with a moving coil or a solid iron rotor. Any location to which the reflected light beam is directed may be addressed independent from the previous position of the light beam. At least two galvanometer scanners may be provided. When the galvanometer scanners are arranged such that each laser beam is directed from the first galvanometer scanner to the second galvanometer scanner, any two-dimensional scanning movement may be possible.

The tasks of the scanning mirror device may also be executed with acousto-optical devices. In these, an acoustic wave is coupled into an acousto-optic material. The frequency of the acoustic wave governs the angle of deflection of a laser beam travelling through the acousto-optic material. By rapidly altering the frequency of the acoustic wave, a fast scanning motion of the laser beam can be achieved.

For marking the object while it is moving relative to the marking apparatus, in another embodiment the control unit is adapted to adjust the deflection means and/or the at least one scanning mirror device according to information on a movement of the object. The object can thus be chased or tracked. It is possible to speed up or slow down a relative movement between the apparatus and the conveying unit moving the object. The speed of the marking process can thus be increased.

According to still another embodiment of the invention, the first and the second set of mapping mirrors are each arranged in a linear array; and each mapping mirror is tiltable. In this embodiment, the pitch between the mapping mirrors of one of the sets of mapping mirrors may be fixed, which allows for employing a common mounting means that holds the mapping mirrors in the linear arrangement, while tilting of the mirrors is still possible. The second set of mapping mirrors may be tilted out of a plane formed by the laser beams that impinge on the first set of mapping mirrors. Positioning means for adjusting the position of at least one of the linear arrays of mapping mirrors may be provided. In particular, the positioning means may displace the common mounting means.

Another embodiment of the inventive apparatus is characterized in that the control unit is adapted for controlling the deflection means to set a degree of convergence or divergence of the laser beams emanating from the deflection means, in particular from the second set of deflection means. In other words, after being redirected with the deflection means, the laser beams do not run in parallel to each other but have a beam separation which is dependent from the distance to the marking apparatus, or, in particular, to the set of deflection means. The deflection means can be adjusted such that a desired pitch between the laser beams is caused at a given distance from the apparatus. The height of a character produced by the laser beams as well as the printing resolution, i.e., the distance between markings caused by neighbouring laser beams on the object, are governed by the separation of the laser beams and can thus also be varied by adjusting the degree of convergence. To this end a fast tilting of the deflection means suffices and there is no need for changing the distance between the deflection means which might be more time consuming.

The lasers may be arranged such that the laser beams exit the lasers in parallel and form a linear arrangement. However, depending on the application, it may be desired to change the orientation of that linear arrangement of laser beams. To this end, the control unit may be adapted to adjust the deflection means such that a linear arrangement of laser beams impinging on the deflection means is rotated, e.g. by 90°, about an axis parallel to the direction of travel of the impinging laser beams. A horizontal arrangement can thus be rotated to a vertical arrangement or vice versa. This may be advantageous as usually signs or characters are to be printed onto the product in either a horizontal or a vertical direction. Hence, the control unit can switch at least between these two important cases. For rotating the linear arrangement of laser beams, the set of deflection means may comprise a first set of mapping mirrors which is used together with at least one or two scanning mirror devices.

According to still another embodiment of the invention, a telescopic device with at least two lenses is provided for global adjustment of the focal lengths of the laser beams. The global adjustment may be understood such that all laser beams of the lasers run through the telescopic device and are thus affected in the same way. The control unit may be adapted to set the telescopic device according to the distance of the object, in particular such that the focal lengths of the laser beams correspond to the distance to the object. Spot sizes of markings produced on the object can be held constant while the object is approaching or moving away from the apparatus. Information on the distance to the object may be supplied to the control unit either from a conveying unit that moves the object and/or by deploying generally known distance measuring means. The telescopic device may be arranged behind the deflection means, as the maximum beam separation between any two laser beams may be reduced by the deflection means. Optical elements of the telescopic device may thus be built smaller.

According to another embodiment of the invention, the control unit is adapted to delay the activation of each laser individually such that, in the case of an object moving relative to the marking apparatus in an object movement direction, at least two laser beams impinge on the object at the same position in the object movement direction.

The timing of the activation of the lasers may be such that all laser beams impinge on the object at the same position in the object movement direction.

Furthermore, regardless of the orientation between the emanating laser beams and the object movement direction, the different laser beams may cause marking spots in a line which is perpendicular to the object movement direction. The length of the line depends on the orientation between the emanating laser beams and the object movement direction.

The lasers may be stacked such that the laser beams emitted by the lasers form an array of laser beams, in particular a linear array with parallel laser beams. Each laser may be a gas laser which comprises resonator tubes that at least partially surround an inner area, that is the resonator tubes form a closed or open ring. The emitted laser beams are directed into the inner area with beam-delivery means, preferably a set of mirrors. It is generally also possible that the beam-delivery means are formed by the output coupler mirrors of the gas lasers. In this case a resonator tube end portion of each gas laser may point into the direction of the inner area. The set of deflection means may then be arranged in the inner area.

Cooling of the resonator tubes is facilitated in that those resonator tubes that are arranged on opposing sides of the closed or open ring are at a maximum distance to each other, while at the same time the overall dimensions of the apparatus are not increased, as optical elements are space-savingly accommodated in the inner area.

In the case that each gas laser comprises resonator tubes that at least partially surround an inner area, and beam delivery means are provided for directing the laser beams emitted by the gas lasers into the inner area, it may be preferred that the beam delivery means are part of the telescopic means. The beam delivery means may comprise one mirror per laser beam, which mirror may form a first optical element of each telescopic means.

Alternatively, the output couplers of the gas lasers for coupling out laser beams may be part of the telescopic means. The output couplers may be partially reflecting mirrors wherein the outer surface, i.e. the surface facing away from the laser gas, of each mirror may generally have any shape. It may therefore be preferred that the shape is such that each output coupler behaves like a first lens of a generally known telescope.

A variant of the invention is concerned with the case of a failed pixel, that means a laser is defective and does not emit a laser beam. For substituting the laser beam of a failed laser, the control unit may be adapted to adjust the deflection means and the telescopic means such that the laser beam of a functioning laser is deflected in the direction of the failed laser beam. The telescopic means are thus controlled to adjust for the path length difference between the failed laser beam and the laser beam used for substituting the former.

In a multiple pass option, the substitute laser beam is successively directed to its regular direction and the direction of the failed laser beam. Alternatively or additionally, a reduced resolution printing may be carried out in case of a pixel failure. To this end, the control unit may be adapted to reduce the resolution of the sign to be marked in the case of a failure of a laser, to activate the functioning lasers to emit laser beams according to the reduced resolution sign, and to set the deflection means and the telescopic means according to the reduced resolution sign.

Another embodiment of the invention is characterized in that each deflection means comprises or consists of an optical waveguide. The optical waveguides may be any flexible waveguides that guide light with the wavelengths emitted by the lasers, in particular infrared light with a wavelength of about 10 m. Examples of optical waveguides are optical fibers or hollow tubes with a reflective inner surface.

Each optical waveguide may be equipped with input coupling optics for directing the impinging laser beam into a core of the optical waveguide in a proper angle. The optical waveguides may also be equipped with output coupling optics comprising in particular at least two lenses for collecting the laser radiation leaving the waveguide. The output coupling optics may determine the laser beam size, focal length and depth of focus. In particular, the output coupling optics may be formed as telescopic means.

In some embodiments, the optical waveguides have the same length. This leads to the spot size and quality of markings caused on the object being more consistent.

The invention further relates to a marking system that comprises a marking apparatus as described above, and which further comprises pivoting means for tilting the marking apparatus relative to an object movement direction.

As will be explained subsequently, by tilting the marking apparatus, it is possible to alter the printing resolution, i.e. the distance between marking spots on the object in a direction perpendicular to an object movement direction. This is governed by the beam separation in the direction perpendicular to an object movement direction. A beam separation in the object movement direction is not detrimental to the printing resolution, as the activation of the lasers can be delayed until the object has moved by as much as the beam separation in the object movement direction.

It is then possible to change the beam separation in the direction perpendicular to an object movement direction by tilting the marking apparatus and thus the arrangement of laser beams. The control unit may be adapted to tilt the marking apparatus with the pivoting means according to a desired printing resolution.

In the case of a linear arrangement of laser beams, the tilt angle between the linear arrangement of laser beams and the object movement direction governs the distance between marking spots on the object in a direction perpendicular to the object movement direction. The distance between the marking spots is at a maximum if the linear arrangement of laser beams is perpendicular to the object movement direction. For setting a smaller distance, the tilt angle can be reduced. Together with properly timing the firing of the lasers, the tilt angle can be set such that the marking spots form a continuous line or separated marking spots. Overlapping marking spots may be produced to cause different intensities of marking spots, e.g. for grey-scale printing. Furthermore, the tilt angle can be zero, resulting in a complete overlap of the marking spots if a corresponding delay between the firing, i.e., activation of the lasers is chosen.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention and various other features and advantages of the present invention will become readily apparent by the following description in connection with the drawings, which are shown by way of example only, and not limitation, wherein like reference numerals refer to substantially alike components:

FIG. 1 shows a schematic diagram of a first embodiment of an inventive marking apparatus;

FIG. 2A to 2C show different views of a first configuration of a set of telescopic means and a set of deflection means;

FIG. 3A to 3C show different views of a second configuration of a set of telescopic means and a set of deflection means;

FIGS. 4A and 4B show different views of a third configuration of a set of telescopic means and a set of deflection means;

FIG. 5 shows still another configuration of a set of telescopic means and a set of deflection means;

FIG. 6 shows a set of telescopic means and a configuration of mapping mirrors of a set of deflection means for rearranging the laser beams into a two-dimensional array;

FIG. 7 shows a marking system according to the invention and an object to be marked moving relative to the marking system; and

FIG. 8A to 8D schematically show an arrangement of laser beams exiting the inventive marking apparatus relative to an object movement direction, and markings produced by the laser beams.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically a first embodiment of a marking apparatus 100 according to the invention. The marking apparatus 100 comprises a plurality of lasers 10 which in the depicted example are gas lasers 10. Other laser technologies may be used instead. Each of the gas lasers 10 can be activated to emit a laser beam that is used to produce a marking on an object (not depicted). For forming and directing the laser beams, the apparatus 100 further comprises optical means 30, 40, 45, 50.

In the example shown, the plurality of gas lasers 10 consists of nine gas lasers 10 a-10 i. In general, a large number of gas lasers 10 is desirable, e.g., at least four or six lasers. Each gas laser 10 comprises resonator tubes 12 that are in fluidic connection to each other. That means, the resonator tubes 12 of one gas laser form a common resonator volume. It is also possible that the resonator tubes 12 of different lasers 10 are in fluidic connection.

In the depicted embodiment, the gas lasers are CO₂ lasers and the laser gas accordingly comprises, amongst others, CO₂, N₂ and He.

The resonator tubes 12 are arranged in the shape of a ring surrounding an inner area or free central space 5 between them. The ring is formed with connecting elements 16 for connecting adjacent resonator tubes 12 belonging to the same laser. The connecting elements 16 are arranged in the corners of the stacked lasers and house mirrors for reflecting laser light from one of the adjacent tubes 12 to the other. Naturally, all mirrors are selected dependent on the laser gas used. In the present case, the mirrors comprise a material reflective in the wavelength region of a CO₂ laser, i.e. medium-IR radiation, primarily at 10.6 μm. For example, a copper mirror and/or a substrate with a coating for increasing reflectivity and/or preventing tarnishing in air may be provided.

In the depicted example, the resonator tubes 12 form a sealed ring in the shape of a rectangle. In general, any other shape that at least partially encloses the inner area 5 may be chosen, such as a triangular, a square or a U-pattern.

The resonator tubes 12 are arranged in the shape of a ring surrounding an inner area or free central space 5 between them. The ring is formed with connecting elements 16 for connecting adjacent resonator tubes 12 belonging to the same laser. The connecting elements 16 are arranged in the corners of the stacked lasers and house mirrors for reflecting laser light from one of the adjacent tubes 12 to the other. Naturally, all mirrors may be selected dependent on the laser gas used. In the present case, the mirrors comprise a material reflective in the wavelength region of a CO2 laser, i.e. medium-IR radiation, primarily at 10.6 pm. For example, a copper mirror and/or a substrate with a coating for increasing reflectivity and/or preventing tarnishing in air may be provided.

The marking apparatus 100 further comprises excitation means (not depicted) at each resonator tube 12 and cooling blocks (not depicted) attached to the resonator tubes 12. There may be one cooling block per side of the cubic arrangement of resonator tubes 12. Thus, each cooling block does not merely cool a single resonator tube but a plurality of resonator tubes 12 of different lasers 10 a-10 i. The cooling blocks may have a plurality of channels through which a cooling fluid can circulate.

The resonator tubes 12 of each laser 10 are arranged in individual, separate flat layers. The lasers 10 are substantially identical and are stacked on top of each other in a parallel manner. The lasers 10 are connected to each other by suitable connecting means, such as bolts, screws or the like.

The rectangular shape of the lasers 10 may be open at one corner. In the depicted embodiment this is the top left corner at which an integrated output flange 17 is provided. At this corner, the laser volume is terminated by a rear mirror 18 for reflecting laser light back inside the tubes 12. The rear mirror 18 may be connected to an end tube 12 which is supported by the integrated output flange 17, or the rear mirror 18 may be attached to the integrated output flange 17.

The other end of the laser volume is terminated at the same corner by an output coupler 13. The output coupler 13 couples out a laser beam and may again be connected to either an end tube 12 or the integrated output flange 17. The output coupler 13 may be a partially reflecting mirror 13 and may also be referred to as partially reflecting output coupler. The emitted laser beams are then directed into the inner area 5 with beam delivery means 14. In the embodiment shown, the beam delivery means 14 comprise at least one mirror 14 arranged at the integrated output flange 17. The laser beams reflected from the beam delivery means 14 enter the inner area 5 through a hole in the integrated output flange 17. Generally it is possible that a common integrated output flange 17 for all lasers 10 is provided. In the depicted embodiment, however, there is one integrated output flange 17 per laser 10 and each integrated output flange 17 exhibits one beam delivery means 14 and one hole through which a respective laser beam can pass.

In the inner area 5, optical means 30, 40, 45, 50 for shaping and deflecting the laser beams are provided. This arrangement advantageously leads to comparably low space requirements. Simultaneously, opposing resonator tubes 12 of one laser are separated by the inner area 5 which facilitates cooling of the tubes 12.

The laser beams coming from the beam delivery means 14, in this case a mirror 14, impinge on a set of telescopic means, or beam shaping means 40, for refocusing the laser beams. The set of telescopic means 40 comprises one lens 40 a-40 i for each laser beam. Additionally each telescopic means 40 comprises another optical element, which, in the depicted case, is constituted by the mirror 14. Other not depicted optical elements may be used instead. With the telescopic means 40 the focuses of the laser beams are set independently from each other. Compared to beam shaping means consisting of only one optical element for adjusting a focus of a laser beam, the telescopic means facilitate the adjustment in that only smaller displacements of the optical elements of the telescopic means are required.

The laser beams then impinge on a set of deflection means 30. In the example shown, the laser beams previously travel through the beam shaping means 40. However, this order may be changed or the single elements of both sets may alternate, i.e. one element of the beam shaping means 40 may be arranged between two elements of the deflection means 30.

It is generally also possible that the beam delivery means 14 form part of the deflection means 30. In this case the beam delivery means 14 may constitute the first set of mapping mirrors. The number of required optical elements may then be reduced.

In the depicted embodiment, the set of deflection means 30 comprises one deflection means 33 a-33 i per laser beam. These deflection means 33 a-33 i may also be referred to as a first set of mapping means 33. In general, the deflection means may be any means that change the propagation direction of a laser beam. In the shown example, the deflection means are mirrors. The mirrors of the set can be positioned independently from one another. Consequently, the arrangement of the laser beams impinging on the deflection means 30 can be altered by adjusting the position of the individual mirrors 33 a-33 i. The latter can thus be referred to as mapping mirrors 33 a-33 i.

The mapping mirrors 33 a-33 i are tiltable and displaceable, that is translationally movable. For tilting the mirrors, each mapping mirror 33 a-33 i is gimbal mounted. A control unit (not depicted) may be adapted to set a desired position of each mapping mirror 33 a-33 i via the gimbals.

After leaving the deflection means 30, the laser beams impinge on a number of common optical elements, i.e. optical elements onto which all laser beams impinge. These may comprise a telescopic device 45 for global adjustment of the focuses of the laser beams. In contrast to the set of telescopic means 40 described above, the telescopic device 45 affects all laser beams equally.

The optical elements in the beam path may further comprise means for altering or homogenizing the intensity profile of a light beam, means for changing a polarisation of the light beams, in particular for achieving a common polarisation over the whole cross section of a light beam, or for depolarising the light beams.

Finally, the laser beams are directed out of the apparatus 100 by a scanning mirror device 50. This device 50 may comprise two galvanometer scanners 50, each having a rotatable common mirror 50 a onto which all laser beams impinge. With two galvanometer scanners 50, any direction of travel can be readily set for the laser beams.

A first arrangement of the set of deflection means 30 and the set of telescopic means 40 is shown in FIG. 2A to 2C from different perspectives.

For beam shaping and collimating the laser beams 90 a-90 i, the set of telescopic means 40 comprises a plurality of telescopic means 40 a-40 i, which may be built identically. Each telescopic means 40 a-40 i may have at least two lenses 41 and 42 which can be offset in the propagating direction of the laser beams 90 a-90 i for adjusting the focus of the respective laser beam 90 a-90 i and thus a spot size on an object to be marked. As there is one telescopic means 40 a-40 i for each laser beam 90 a-90 i, the beams can also be adjusted for path length differences.

After passing the telescopic means 40 a-40 i, the laser beams 90 a-90 i impinge on a set of deflection means 30 which comprises a first and a second set of mapping mirrors 33, 34. That is, each light beam 90 a-90 i is directed from a first mapping mirror 33 a-33 i to a second mapping mirror 34 a-34 i. The mapping mirrors of the first set 33 and those of the second set 34 are each arranged in a linear array 35, 36.

In the example shown, the laser beams 90 a-90 i are mapped with the set of deflection means 30 such that a linear arrangement of laser beams is rotated, e.g. by 90°. This configuration can thus also be referred to as a horizontal to vertical pixel mapper. The first and second sets of mapping mirrors 33, 34 are arranged in one plane and perpendicular to one another.

The mapping mirrors 33, 34 can be adjusted with the gimbal mounts such that the outgoing laser beams 90 a-90 i run in parallel in the desired direction.

A scanning motion of the laser beams 90 a-90 i for printing a sign on an object may be performed with the second set of mapping mirrors 34. Alternatively, the second set of mapping mirrors 34 may direct the laser beams 90 a-90 i to a scanning mirror device.

FIG. 3A to 3C show different schematic views of another configuration of the set of telescopic means 40 and the set of deflection means 30.

This configuration differs from the previous one in the arrangement of the first and second set of mapping mirrors 33, 34. In the present case, the sets 33, 34 form linear arrays which—unlike the former configuration—are not in one plane. Rather, the two linear arrays are at an angle, in this case 45°, to reduce the space between the laser beams 90 a-90 i. At the same time, the linear arrangement of laser beams 90 a-90 i is rotated by 90°.

In this embodiment, each telescopic means comprises one lens and a mirror which also serves as a deflection means 33 a-33 i. If the mirror 33 a-33 i is moved for changing the direction of travel of the respective laser beam 90 a-90 i, the lens of the telescopic means may be moved accordingly such that a focus of the laser beam 90 a-90 i remains unaltered.

FIGS. 4A and 4B show still another configuration of the telescopic means and the mapping mirrors 33, 34. As in the previous cases, the configuration depicted in FIGS. 4A and 4B exhibits mapping mirrors of a first and a second set 33, 34, each set being arranged in a linear array 35, 36. In the incident embodiment, however, the mapping mirrors of the second set 34 are tilted such that the reflected laser beams 90 a-90 i converge, that is the beam separation is further reduced depending on the desired separation at the desired distance from the apparatus for varying the resolution and dimensions of markings being produced.

The mapping mirrors of the second set 34 may be tiltable via gimbal mounts by the control unit. The mapping mirrors of the first set 33 may either be fixed such that a displacement of these mirrors is not possible during a printing operation, or the mirrors may be gimbaled as well.

In the embodiments shown in FIGS. 2A to 4B, a scanning motion of the laser beams 90 a-90 i may be performed by tilting the mapping mirrors 34 a-34 i of the second set of mapping mirrors 34. Scanning devices such as galvanometer scanners with a common mirror for redirecting all laser beams 90 a-90 i are in this case not present: However, it may also be useful to provide such scanning devices.

For setting the deflection means to any of the configurations shown in the FIGS. 2A to 2C, 3A to 3C, and 4A and 4B, a control unit may be provided.

FIG. 5 shows schematically another arrangement of mapping mirrors 33 a-33 i. Here, the set of deflection means 30 consists of a single set of mapping mirrors 33. A linear array of laser beams 90 a-90 i passing through the telescopic means 40 a-40 i is reflected from the mapping mirrors 33 a-33 i such that the beam distance between the laser beams 90 a-90 i is reduced. The beam distance may be the same between any two neighbouring reflected laser beams 90 a-90 i. In the example shown, the line of laser beams 90 a-90 i is not rotated out of a plane formed by the mapping mirrors 33 a-33 i and the telescopic means 40 a-40 i. Tilting the mapping mirrors 33 a-33 i such that the reflected laser beams 90 a-90 i run out of said plane would result in a change of the beam distance or separation. Therefore, in this embodiment a scanning motion of the laser beams 90 a-90 i is not performed with the set of deflection means 30. Rather at least one scanning device as shown in FIG. 1 is provided.

Reducing the beam separation allows the design of the stack of gas lasers to be optimized for thermal cooling and RF excitation without penalizing the resolution or character size of the print, i.e., a larger separation of the gas lasers can be compensated.

FIG. 6 depicts a configuration of the mapping mirrors for rearranging the laser beams 90 a-90 i into a two-dimensional array of laser beams, e.g. a three by three square. Once again, the set of deflection means 30 comprises a first and a second set of mapping mirrors 33, 34. In the example shown, the telescopic means 40 a-40 i are arranged between the first and the second set of mapping mirrors 33, 34. However, the telescopic means 40 a-40 i may instead be arranged prior to the first set 33 or after the second set 34 of mapping mirrors.

Also shown in FIG. 6 are the beam delivery means which redirect the light beams 90 a-90 i coming from the lasers to the first set of mapping mirrors 33. The beam delivery means are formed by a set of mirrors 14 a-14 i, i.e. one beam delivery means per laser beam. In other embodiments, this set may be substituted by one long mirror.

The mapping mirrors 34 a-34 i of the second set are arranged in a two-dimensional array such that the reflected laser beams 90 a-90 i are mapped in a two-dimensional array. In some cases, the distance between the laser beams 90 a, 90 i being most distant to one another is greatly reduced, especially in comparison to any linear arrangement of the laser beams. The beams are more tightly packed and therefore go through the central portion of optical elements, such as focusing optics 45. As optical aberrations occur mainly in the outer regions of optical elements, the two dimensional arrangement has the benefit of improved focusing and beam quality of the laser beams. Especially the outer most laser beams suffer less distortion compared to a linear arrangement of the laser beams. Furthermore, the size of optical elements can be reduced, leading to lower overall costs.

FIG. 7 shows schematically a marking system 120 and an object 1 to be marked.

The object 1 is moved in an object movement direction 2 and is depicted in three different positions, that is at three different points in time. The marking system 120 comprises a marking apparatus 100 and pivoting means 110 for tilting the marking apparatus 100.

The marking apparatus 100 may comprise any components as described above, e.g. deflection means constituted by two sets of mapping mirrors each arranged in a linear array. As shown in FIG. 7, a control unit 20 is also provided as well as positioning means 60. The latter serves for positioning the linear arrays of mapping mirrors. The individual mapping mirrors may be fixed within the respective array such that they cannot be displaced but tilted, e.g. with gimbal mounts.

The marking apparatus 100 emits a plurality of laser beams, three of which 90 a, 90 b, 90 c are shown in FIG. 7. As the object 1 moves, the laser beams 90 a, 90 b, 90 c are correspondingly redirected.

Depending on the shape and the position of the object 1, the distance between the apparatus 100 and the object 1 may change by as much as indicated with the reference sign d. Furthermore, at one point in time, the distance may be different for each laser beam 90 a, 90 b, 90 c. Still, the spot sizes of the laser beams 90 a, 90 b, 90 c on the object 1 are to be equal. To this end, beam shaping means as described above are provided and adjusted by the control unit 20.

In the following, the function and benefit of the pivoting means 110 are explained with reference to FIG. 8A to 8D, each of which shows schematically the arrangement of laser beams 90 a-90 i emitted by the apparatus 100 relative to an object movement direction 2.

In FIG. 8A the linear arrangement of laser beams 90 a-90 i is parallel to the object movement direction. At least two of the laser beams 90 a-90 i impinge on the same spot 80 on the object 1 by individually delaying the firing of the gas lasers. The delay may be set to be equal to the separation between the laser beams 90 a-90 i divided by the speed of the object or the speed of the object in the direction of the linear arrangement of laser beams.

In the FIG. 8B to 8D the linear arrangement of laser beams 90 a-90 i is angularly tilted to the direction of travel 2 of the object by an angle α. This tilt angle α may be set with the pivoting means 110. Together with a delay of the firing, the tilting leads to the printing of a line formed by dots 81-89. The dots 81-89 may overlap, as in FIG. 8B, or may be separated as in FIGS. 8C and 8D. The length of the line thus produced is determined by the tilt angle α between the laser beams 90 a-90 i and the object movement direction 2. The size of each dot 81 to 89 and thus the width of the line can then be controlled with the beam shaping means.

The described marking apparatus allows for shaping each laser beam individually via a set of telescopic means. Furthermore, the beam separation and the arrangement of a plurality of laser beams may be changed with a set of deflection means. Space requirements may be minimized by arranging the optical elements, in particular those of the telescopic means and the deflection means, within an area surrounded by the gas lasers. 

The invention claimed is:
 1. A marking apparatus for marking an object with laser light, comprising a plurality of lasers, wherein each laser is a gas laser and comprises resonator tubes, wherein the plurality of lasers are arranged in the shape of a ring that at least partially surrounds an inner area; a control unit configured to individually activate each of the lasers in the plurality of lasers to emit a laser beam according to a sign to be marked; a telescopic device, onto which all laser beams impinge, for global adjustment of the focuses of the laser beams, wherein the telescopic device has at least two optical elements for adjusting a focus of impinging laser beams, and wherein the telescopic device is located within the inner area; a set of deflection means for directing the laser beams toward the object to be marked, wherein the set of deflection means comprises at least one deflection means per laser beam for flexibly rearranging the laser beams into any desired array of laser beams, and each deflection means is at least one of: individually adjustable in its deflection direction or individually shiftable, wherein the marking apparatus further comprises: a set of telescopic means comprising at least one telescopic means per laser beam, wherein the set of telescopic means are separate components from the telescopic device, each telescopic means is adjustable for individually setting a focal length of the respective laser beam, the control unit is adapted to control the telescopic means to compensate for path length differences between the laser beams due to the arrangement of the deflection means; at least one scanning mirror device is provided which comprises a common mirror onto which all laser beams coming from the set of deflection means impinge, and the control unit is adapted for pivoting the scanning mirror device; and beam delivery means which comprise at least one optical element for deflecting impinging laser beams, the at least one optical element being arranged such that laser beams emitted by the lasers are deflected into the inner area, and the at least one optical element of the beam delivery means is part of the telescopic means for individually setting the focal length of an impinging laser beam.
 2. The marking apparatus according to claim 1, wherein the at least two optical elements of the telescopic device are at least two lenses or curved mirrors, the distance between which being adjustable for setting the focal length.
 3. The marking apparatus according to claim 1, wherein each deflection means is one of: a mapping mirror or an optical waveguide.
 4. The marking apparatus according to claim 1, wherein each telescopic means comprises a mirror which is one of the mapping mirrors and an optical element which is displaceable relative to the mapping mirror.
 5. The marking apparatus according to claim 1, wherein each laser comprises an output coupler for coupling out a laser beam, and the output couplers of the lasers are part of the telescopic means.
 6. The marking apparatus according to claim 5, wherein for substituting the laser beam of a failed laser, the control unit is adapted to adjust the deflection means and the telescopic means such that the laser beam of a functioning laser is deflected in the direction of the failed laser beam.
 7. The marking apparatus according to claim 1, wherein the control unit is adapted to: reduce the resolution of the sign to be marked in the case of a failure of a laser, activate the functioning lasers to emit laser beams according to the reduced resolution sign, and set the deflection means and the telescopic means according to the reduced resolution sign.
 8. The marking apparatus according to claim 1, wherein the deflection means are adjusted such that a beam separation between the laser beams is reduced.
 9. The marking apparatus according to claim 1, wherein the set of deflection means comprises a first and a second set of mapping mirrors, each set of mapping mirrors comprises at least one mapping mirror per laser beam, and the first set of mapping mirrors directs the laser beams onto the second set of mapping mirrors.
 10. The marking apparatus according to claim 9, wherein the first and the second set of mapping mirrors are each arranged in a linear array; and each mapping mirror is tiltable.
 11. The marking apparatus according to claim 1, wherein the control unit is adapted for controlling the deflection means to set a degree of convergence or divergence of the laser beams emanating from the deflection means.
 12. The marking apparatus according to claim 1, wherein each deflection means comprises an optical waveguide, and the optical waveguides have the same length.
 13. The marking apparatus according to claim 1, wherein the control unit is further adapted to adjust the set of deflection means such that the laser beams of at least two lasers are directed onto a common spot.
 14. A marking system comprising: the marking apparatus according to claim 1, wherein the marking apparatus is pivotably supported to be tiltable relative to an object movement direction of the object to be marked.
 15. The marking apparatus according to claim 1, the telescopic device being arranged such that all laser beams emitted by the plurality of lasers impinge on each of the at least two optical elements for equally adjusting the focus of each laser beam.
 16. The marking apparatus according to claim 1, wherein the ring has a substantially rectangular shape.
 17. A marking apparatus for marking an object with laser light, comprising a plurality of lasers, wherein each laser is a gas laser and comprises resonator tubes, wherein the plurality of lasers are arranged in the shape of a ring that at least partially surrounds an inner area; a control unit configured to individually activate each of the lasers in the plurality of lasers to emit a laser beam according to a sign to be marked; a telescopic device with at least two optical elements for adjustment of a focus of impinging laser beams, the telescopic device being arranged such that all laser beams emitted by the plurality of lasers impinge on each of the at least two optical elements for equally adjusting the focus of each laser beam, and wherein the telescopic device is located within the inner area; a set of deflection means for directing the laser beams toward the object to be marked, wherein the set of deflection means comprises at least one deflection means per laser beam for flexibly rearranging the laser beams into any desired array of laser beams, and each deflection means is at least one of: individually adjustable in its deflection direction or individually shiftable, wherein the marking apparatus further comprises: a set of telescopic means comprising at least one telescopic means per laser beam, wherein the set of telescopic means are separate components from the telescopic device, each telescopic means is adjustable for individually setting a focal length of the respective laser beam, the control unit is adapted to control the telescopic means to compensate for path length differences between the laser beams due to the arrangement of the deflection means, and at least one scanning mirror device is provided which comprises a common mirror onto which all laser beams coming from the set of deflection means impinge, and the control unit is adapted for pivoting the scanning mirror device; and beam delivery means which comprise at least one optical element for deflecting impinging laser beams, the at least one optical element being arranged such that laser beams emitted by the lasers are deflected into the inner area, and the at least one optical element of the beam delivery means is part of the telescopic means for individually setting the focal length of an impinging laser beam.
 18. The marking apparatus according to claim 17, wherein the ring has a substantially rectangular shape. 